Spatial and Temporal Change of Urban Vegetation Distribution in Beijing
Urban vegetation is one of the important infrastructural components of any urban ecosystem. The existence of well-distributed and abundant vegetation cover in cities can provide many benefits for city dwellers. The most obvious benefit to the public is aesthetic. Trees, shrubs, and lawns add natural color, shape, and texture to the rectilinear concrete and asphalt surfaces in cities and conceal unpleasant spots from view (Miller, 1997). Urban vegetation can also generate direct economic benefits by producing timber, fruits, fuel wood, cut flowers, and many other goods (Kuchelmeister and Braatz, 1993). However, urban vegetation also supplies other more indirect benefits by providing environmental services that enhance quality of life in cities (see Chapter 16). Urban vegetation can filter air pollutants, sequester CO2, shade and shelter homes from sun and wind, intercept urban runoff, and provide habitat for wildlife (Miller, 1997; Xiao et al., 1998; McPherson and Simpson, 1999; Nowak et al., 2000).
Various studies have been conducted to quantify the benefits and costs of urban vegetation (McPherson, 1997, 2000, 2003; McPherson et al., 1999; Nowak and Dwyer, 2000). Among their conclusions was the realization that environmental services provided by urban vegetation are strongly related to the structure of that vegetation. The type of vegetation, size, and spatial distribution of urban vegetation are structural factors that mattered most to the degree of benefit obtained. However, urban vegetation management in China places major emphasis on the absolute quantity of green space, such as total area of urban vegetation, total canopy cover, and per capita vegetation cover, and overlooks other structural attributes of urban vegetation as indicators of improvement in urban greening plans. Among those neglected structural characteristics is the spatial distribution pattern of urban vegetation. One good example of why and how this neglect comes about during planning and management is the misrepresentation of statistics to artificially report improvement in vegetation cover. To boost the statistics of vegetation cover in the city, some municipal governments combine the small amount of green cover existing in the densely populated central city districts with the high vegetation cover in rural areas at the urban fringe to get a high average urban canopy cover. Accepting such simplistic indexes as a basis for planning green space does not provide incentive to create more green space in densely populated areas where the public needs it most (see Chapter 9). These simple statistics are also used because they are relatively easy to obtain as compared to data dealing with spatial distribution. Studies that shed light on the spatial distribution of vegetation in cities can help to counter the problem mentioned above and improve the effectiveness of urban greening practices for cities in China and other parts of the world.
KeywordsRoot Mean Square Error Vegetation Cover Canopy Cover Green Space Urban Forest
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